In the process of drilling a fluid producing well, such as an oil well, it is common to determine the nature of a zone or formation of interest before completion of the well by conducting a drill stem test. It is important in such a test to obtain fluid samples as well as to determine other significant factors such as the permeability of the formation and the volume and pressure of the reservoir. To obtain a more complete profile of the well and the surrounding formation, the pressure build-up under down hole shut-in conditions is also usually measured after conducting the drill stem test.
To conduct a drill stem test, the test equipment or tool string is normally assembled on a drill string which is lowered into the bore. A packer in the drill string is seated at a predetermined depth and functions to seal off the hole below it A perforating gun on the tool extending below the packer is actuated to produce perforations in the well bore to allow fluid from the surrounding formation to flow into the bore. Fluid enters the tool below the packer and flows up the drill string. Suitable instruments in the tool string record the pressure of the fluid.
If the fluid is under enough pressure to naturally flow to the surface the drill stem test can be routinely handled. If, however, there is insufficient reservoir pressure or solution gas, or a combination of the two, to cause the fluid to flow naturally to the surface, it is desirable to lift the fluid by some other means. This normally requires the drill string to make separate trips down the bore, one to perforate the casing and another to test the fluid, or it can require multi-trip wire line runs in the well. Also, by testing the well on separate trips from the perforation operation, testing on later runs requires the well to be killed. These multiple trips with wire line or drill string add significantly to the cost of the well, since each trip is quite expensive.
It would be advantageous in a drill stem test involving formation fluid which is under insufficient pressure to naturally flow to the surface, to be able to lift or convey the formation fluid to the surface in the same trip of the drill string used for the purpose of perforating the well casing. I would also be advantageous to be able to do so without interfering with or preventing a down hole shut-in pressure test.